Build Lighting 'resets' lightmap changes in StaticMesh Editor

Hi everyone,

I have a problem (or maybe do something wrong) with common error ‘Object has wrapping UVs’.
First of all I create sketch-level from BSP-brushes, set textures, and then convert BSP to StaticMeshes. And got this problem (‘Object has wrapping UVs’).
Ok, I google for solution for this problem, and found it.

After changing lightmap index from 0 to 1 → Apply Changes → Save Mesh I see this:

Woohoo, that’s what I need! Just rebuild lighting… I press ‘Build All’ wait, and… WHAT???
I see this:

I open every mesh in MeshEditor and all settings was correct:

I try change ‘Destination Lightmap Index’ to 0 or 2, but this changes don’t affect on final relsult (problem2.png).

This is bug or I do something wrong?


  1. Source Lightmap - always must be 0. Because this main Color channel. Lightmap always applied to this channel.

  2. Destination Lightmap Index - always must be 1. Because this is channel only for Lightmap. And always used for build light.

Thank you for your answer, but as I see in Wiki:

changing ‘Source ligthmap index’ it’s correct way to fix ‘Overlapping UVs’.

Lightmap always use UV 1 (secondary UV channel). UE4 always read info from Lightmaps from UV1. ‘Overlapping UVs’ appear if secondary channel empty or your mesh have only one first UV channel.

Converting BSP in static mesh have bug. You need open mesh editor and input any value in Light Map Resolution. This parameter located in Static Mesh Setting in Details. But you changed Min Lightmap Resolution this is no right. In my previous picture Light Map Resolution marked with number 3.

I set all values as you advised, and have this in StaticMesh Editor:

  • UV Channel 0 (wrong)

  • UV Channel 1 (seems fine)

And in editor this:

As in initial situation it’s BSP converted to Static Mesh.

And in all cases any changes in StaticMesh Editor makes scene looks good, but only before pressing ‘Build’ button.

Ok, as I understand my problem was be in my wish: Create Laaarge Mesh from BSP (it’s works wrong in UE4 =( ). I provide some tests in small objects and all works fine.